Diurnal lipid and mucus production in the staghorn coral Acropora acuminata

Abstract

Net 14C-accumulation into lipids of Acropora acuminata was rapid and increased with light intensity. Dark 14C-incorporation was less than 1% noon maximum. Structural lipids were the first radioactively labelled lipid types showing linear 14C-uptake kinetics. Storage lipids showed non-linear, power-curve kinetics for 14C-uptake. The rate of 14C-incorporation into triglycerides and wax esters was maximal during early afternoon and at midday, respectively. Electron microscopic evidence is given for zooxanthellae being primary sites for synthesis of lipids which are exuded from chloroplasts and transferred to animal tissues. Free lipid droplets and crystalline inclusions (wax ester) were common in animal tissues, the inclusions being often associated with mucus-producing cells. The diurnal rate of mucus production was constant. However, 14C-mucus-lipid production showed a light-dependent diurnal pattern and accounted for 60 to 90% total 14C of mucus during periods of photosynthetically-saturating light. Here, 14C was primarily associated with wax esters which were always present in the mucus-lipid. 14C-triglycerides occur in mucus released only during the day. Lipid and mucus synthesis is discussed in relation to the carbon budget of A. acuminata, in which mucus represented a loss of 40% net C fixation.

Keywords

Lipid Carbon Budget Structural Lipid Diurnal Pattern Mucus Production

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